The use of Nasal Continuous Positive Airway Pressure (nasal CPAP) to treat Sleep Disordered Breathing (SDB) was pioneered by Sullivan, e.g., see U.S. Pat. No. 4,944,310. Apparatus for providing nasal CPAP typically comprises a source of air at positive pressure (for example provided by a blower or flow generator at 3-30 cmH2O), some form of patient interface or respiratory mask system (for example a nasal or full-face mask system), and an air delivery tube.
Respiratory mask systems typically include some form of cushioning element, a sealing element and some form of stabilizing element (for example, a frame and headgear). The cushioning and sealing elements may be formed in one piece and collectively referred to as a “cushion”, or more than one piece, or may be separate structures. Cushioning and sealing elements may be formed from different portions of a single structure. Headgear may include an assembly of soft, flexible, elastic straps. Headgear may be constructed from a composite material such as foam and fabric, and may include a stiffening element.
The frame may be a rigid or semi-rigid structure that allows for the connection of the cushion, headgear and air delivery tube. The frame can be made of a hard material such as polycarbonate, a semi-rigid material such as a high durometer silicone (e.g. 80 Type A durometer) or polypropylene, or various other materials alone or in combination, such as a combination of a rigid frame skeleton and a soft chamber defining material.
Much mask design effort is directed towards improving the comfort of masks, which among other benefits, can help lead to better compliance and efficacy of therapy. A range of commercial mask systems are known including the MIRAGE mask, manufactured by ResMed Limited.
Also, the performance or properties of a mask may be measured or evaluated using different tests. However, the accuracy of any test may depend on one or more parameters of the sample and/or equipment. Therefore, tests and testing equipment are desired to reduce or eliminate testing variances.